Fold in parser, main loop, and support.

.hgignore

@@ -1,4 +1,5 @@
 .*\.pyc$
+.*\.swp$
 .hypothesis
 .pytest_cache
 .vscode

thun/gnu-prolog/thun.pl

@@ -1,6 +1,3 @@
-:- dynamic(func/3).
-:- discontiguous(func/3).
-
 /*
     Copyright  2018, 2019 Simon Forman
 
@@ -20,6 +17,12 @@
     along with Thun.  If not see <http://www.gnu.org/licenses/>.
 
 */
+:- dynamic(func/3).
+:- discontiguous(func/3).
+
+:- initialization(loop).
+
+
 /*
 Interpreter
 thun(Expression, InputStack, OutputStack)
@@ -35,7 +38,7 @@ thun([Combo|E], Si, So) :- combo(Combo, Si, S, E, Eo), thun(Eo, S, So).
 
 thun([Unknown|E], Si, So) :-
     damned_thing(Unknown),
-    write("wtf? "),
+    write(`wtf? `),
     write(Unknown), nl,
     So = [[Unknown|E]|Si].
 
@@ -102,6 +105,70 @@ Definitions
 def(x, [dup, i]).
 
 
+/*
+Parser
+*/
+
+joy_parse([T|S]) --> blanks, joy_term(T), blanks, joy_parse(S).
+joy_parse([]) --> [].
+
+joy_term(N) --> num(N), !.
+joy_term(S) --> [0'[], !, joy_parse(S), [0']].
+joy_term(A) --> chars(Chars), !, {atom_codes(A, Chars)}.
+
+
+/*
+Main Loop
+*/
+
+loop :- line(Line), loop(Line, [], _Out).
+
+loop([eof],  S,   S) :- !.
+loop( Line, In, Out) :-
+  do_line(Line, In, S),
+  write(S), nl,
+  line(NextLine), !,
+  loop(NextLine, S, Out).
+
+
+do_line(Line, In, Out) :- phrase(joy_parse(E), Line), thun(E, In, Out).
+do_line(_Line, S,   S) :- write('Err'), nl.
 
 
 
+% Line is the next new-line delimited line from standard input stream as
+% a list of character codes.
+
+line(Line) :- get_code(X), line(X, Line).
+
+line(10,      []) :- !.  % break on new-lines.
+line(-1,   [eof]) :- !.  % break on EOF
+line(X, [X|Line]) :- get_code(Y), !, line(Y, Line).
+
+
+chars([Ch|Rest]) --> char(Ch), chars(Rest).
+chars([Ch])      --> char(Ch).
+
+char(Ch) --> [Ch], { Ch \== 0'[, Ch \== 0'], Ch >= 33, Ch =< 126 }.
+
+
+blanks --> blank, !, blanks.
+blanks --> [].
+
+blank --> [32].
+
+
+% TODO: negative numbers, floats, scientific notation.
+
+num(N) --> digits(Codes), !, { num(N, Codes) }.
+
+num(_, []) :- fail, !.
+num(N, [C|Codes]) :- number_codes(N, [C|Codes]).
+
+
+digits([H|T]) --> digit(H), !, digits(T).
+digits([]) --> [].
+
+digit(C) --> [C], { nonvar(C), C =< 57, C >= 48 }.
+
+